Event Handler to display on multiple textbox at different time

How do you display data into textboxes one after another as the background code get them when button_click is clicked? I am trying to write code in C# to display reading voltage from power supply, the program work but all the different textboxes display all the measurement at the end of the test instead of line by line or textbox1 then texbox2 and so on. IU is created with Forms. Can anyone help with this please.